[PATCH v7 1/4] fixp-arith: add a linear interpolation function

[Craig Tatlor <ctatlor97@gmail.com>]

Adds a function to interpolate against two points,
this is carried arount as a helper function by tons of drivers.

Signed-off-by: Craig Tatlor <ctatlor97@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
 include/linux/fixp-arith.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/fixp-arith.h b/include/linux/fixp-arith.h
index d4686fe1cac7..b9e2bb59a734 100644
--- a/include/linux/fixp-arith.h
+++ b/include/linux/fixp-arith.h
@@ -153,4 +153,24 @@ static inline s32 fixp_sin32_rad(u32 radians, u32 twopi)
 #define fixp_cos32_rad(rad, twopi)	\
 	fixp_sin32_rad(rad + twopi / 4, twopi)
 
+
+/**
+ * fixp_linear_interpolate() - interpolates a value from two known points
+ *
+ * @x0: x value of point 0
+ * @y0: y value of point 0
+ * @x1: x value of point 1
+ * @y1: y value of point 1
+ * @x: the linear interpolant
+ */
+static inline int fixp_linear_interpolate(int x0, int y0, int x1, int y1, int x)
+{
+	if (y0 == y1 || x == x0)
+		return y0;
+	if (x1 == x0 || x == x1)
+		return y1;
+
+	return y0 + ((y1 - y0) * (x - x0) / (x1 - x0));
+}
+
 #endif
-- 
2.17.0